Conventionally, when a forging raw material in a preheated state is subjected to warm forging or hot forging using a forging press, forging is performed by preheating forging dies and also a forging die holder holding the dies so as not to degrade the plastic deformability of the forging raw material (see, e.g., Japanese Unexamined Patent Application Publication No. Hei 08 (1996)-206768 (FIGS. 1, 2A, and 2B)).
In the forging die holder described in Japanese Unexamined Patent Application Publication No. Hei 08 (1996)-206768 (FIGS. 1, 2A, and 2B) mentioned above, a plurality of parallel grooves each having a U-shaped cross-sectional shape are formed in the longitudinal side surfaces of the die holder, and resistance heaters (sheathed heaters) each formed of a resistance heating element are inserted into the grooves, and covered with a heat insulator material. In the longitudinal side surfaces of the die holder, in the vicinity of the resistance heaters (heaters), a plurality of temperature sensors are disposed along the resistance heaters.
To the lateral side surface of the die holder described in Japanese Unexamined Patent Application Publication No. Hei 08 (1996)-206768 (FIGS. 1, 2A, and 2B), a receptacle box including a lid open/close sensor is attached. In the forging die holder, the resistance heaters and the temperature sensors are provided in the side surfaces of the die holder so that a heating device controls the temperature of heating performed with the resistance heaters based on measurement data by the temperature sensors.